program Project2;

{$APPTYPE CONSOLE}

uses
  SysUtils;

function Max(A, B, C : Integer) : Integer;
begin
   if ((A >= B)  and (A >= C)) then
     Max := A    ;
   if((B >= A) and (B >= C)) then
     Max := B    ;
   if((C >= A) and(C >= B)) then
     Max := C;
end;

function max2(A, B: Integer) : Integer;
begin
  if(A > B)   then
     max2 := A
  else
     max2 := B;

end;

function Min(A, B, C : Integer) : Integer;
begin
   if ((A <= B)  and (A <= C)) then
     Min  := A    ;
   if((B <= A) and (B <= C)) then
     Min := B    ;
   if((C <= A) and(C <= B)) then
     Min := C;
end;

var
  x1, x2, x3, y1, y2, y3: Integer;

begin
  readln(x1, y1, x2, y2, x3, y3);
  write(Abs((x1 - x3) * (y2 - y3) - (x2 - x3) * (y1 - y3)) / (2 + 0.0));
  Readln;
end.
